Occasionally, the battery in the bike does not charge.
Cause 1
Kontaktprobleme zwischen dem Akku und der Rosenberger Ladebuchse im Akkufach oder der Ladebuchse des Stromers. Ursache sind Korrosion, Anwendung von Kontakt-Sprays/Fetten, kleine Metallpartikel (Stecker und Buchse sind magnetisch) oder Defekte der Pins für die 12 V Versorgung des Omnis oder der CAN-Bus Verbindung.

Cause 2
The 'Charching Section' on the controller is defective.

The only solution here is to replace the controller. A repair is not possible.
Handling - Inserting the battery
The following procedure can help to ensure that the battery is positioned correctly in the battery compartment.
Slide the battery down the battery compartment cover. Press the flap closed a little, the battery will slide about 1 cm down into the Rosenberger charging socket. Then fold the battery retaining clip into the groove at the top of the battery compartment cover and close the battery compartment with a little swing.
See also PROBLEMS - AKKU - 'Battery not charging - deep discharged?
See also ERRORS - AND WARNINGS - ‚E 21041C - Battery not charging‘